[Sema] Implement Core 2094: Trivial copy/move constructor for class with volatile member

Summary: This patch implements http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#2094 which reverts Core 496.

Reviewers: rsmith

Reviewed By: rsmith

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D32984

llvm-svn: 302593